Method of producing permanent magnets



METHOD OF PRODUCING PERMANENT MAGNETS Max Baermann, Bensherg-Wulfshof, Germany No Drawing. Filed Feb. 5, 1954, Ser. No. 408,611 Claims priority, application Germany Feb. 6, 1953 13 Claims. (Cl. 29-1556) This invention relates to a method of producing permanent magnets by pressing anisotropic pulverulent permanent magnet materials with a binding agent.

In the production of permanent magnet bodies by pressing pulverulent permanent magnet materials with a binding agent attempts have been made to utilise the advantages offered by the anisotropy of certain materials as regards the magnetic values. It has therefore already been proposed to press such materials in moulds which are under the influence of a powerful magnetic field. This method, however, has not become established in practice, because the high magnetic values of anisotropic materials can only be maintained to a slight extent in this manner. The reason for this resides in the fact that the friction of the individual particles within the pressed mass filling the mould is much too great to be capable of being overcome by the forces which are developed by the magnetic moment of the very small particles of permanent magnet material even under the action of the most powerful fields. The orientation of the particles will therefore always remain only very incomplete, with this known method, so that a considerable proportion of the magnetic material particles within the pressed mass re mains precisely with its unfavourable magnetic axis in the direction of the desired magnetisation, and thus cancels out the advantage which the few orientated parts can offer.

The present invention aims at obviating these difiiculties by orientation of substantially all permanent magnet constituent parts of the pressed mixture in their most favourable direction. To this end, the present invention consists in sprinkling a mixture of magnet material and binding agent, under the constant action of a magnetic field directed according to the direction of flux in the finished magnet, into a mould, and consolidating the mixture into a cohesive body. The magnetic field thus acts upon the permanent magnetic constituent parts of the pressed mixture at a moment when practically falling freely they are still 'freely orientable without overcoming appreciable frictional forces. Thus the constituent parts pile up in a state wherein they are already oriented, so that the friction between the particles now occurring in this heaped state prevents any de-orientation.

In this method also it has proved advantageous first to form the magnet body into tablets and subsequently to press it finally if desired, in a manner known per se. For reasons of pressing technique it is here advantageous to bring the tablets into approximately the final shape of the finished magnet in the plane perpendicular to the pressing direction.

If the desired permanent magnet body is to be of a relatively great height when pressed, it is advantageous according to the invention to make the tablets substantially lower in height, since thus in the consolidation of the tablets the de-orienting forces can be kept smaller, and then further to work up a plurality of tablets into a unitary pressing, taking into consideration the preferred magnetic direction.

2,955,53 Patented Dec. 27, 1960 The same effect can be achieved in accordance with the invention by filling the tablet mould only partially, then consolidating the moulding mass therein, and repeating this operation until the desired tablet height has been achieved. This layer-wise production of the tablets ofiers further advantages for the maintenance of the preferred magnetic direction.

It has also appeared, however, that in the case of simpler magnet shapes in certain circumstances the pretableting can be dispensed with, the magnet body being compacted layer-wise in a manner similar to that described above, by partial fillings of the pressing mould, and then being immediately finally pressed. It must here be ensured, however, that the setting time for the binding agent is long enough to prevent premature setting of individual layers.

Irrespective of which of the above-described possibilities of the method according to the invention is used, it is advantageous to make the direction of the magnetic field substantially transverse to the pressing direction, since by this means the greatest guarantee is given that the particles will not change their direction during consolidation.

As permanent magnet materials for carrying out the method according to the invention there may naturally be used all those the anisotropy of which is sufficiently great to justify the use of such a method. This is the case with the known anisotropic alloys of the Al-Ni group or Al-Ni-Co group, as in the case of powders of other ferromagnetic materials produced predominantly by physical-chemical or chemical methods, wherein the particle size still permits the elementary magnetic properties of the Weiss zones to appear, that is to say is less than about 0.1g. Naturally a number of materials of the magnetic oxide group are suitable for this method. For this purpose all oxides or oxide mixtures of high magnetic value can be used. It is here irrelevant by which method these oxides are produced, provided only the necessary chemical composition and particle size of the powder are obtained. Here those methods commencing, with or without the aid of electrolysis, with the corresponding formates or oxalates appear to be especially suitable.

The mixing of materials of the groups named above can also offer special advantages under certain conditions.

Where metallic oxides are used as permanent magnet material for the pressing mixture, it may be of especial advantage in accordance with the invention to subject these metallic oxides, before or during the mixing With the binding agent, to a heat treatment, and here also, if desired, to permit a magnetic directing field to act upon the material. If in this heat treatment, which may possibly be effected repeatedly, solidification of the powder due to fritting or sintering cannot be avoided, a sufficiently small particle size must be regained by grinding, before further working-up.

In general, the metallic oxides assume a special position in carrying out the method according to the invention, in that in their case possibly the magnetic orienting field can be extraordinarily small, and may even be dispensed with entirely in certain circumstances. It has in fact appeared that in the case of the method of working-up such materials which is usual nowadays, that is to say predominantly the oxides of iron, manganese, barium, etc., or mixtures thereof, the small grain size originally obtained by chemical or other methods almost always increases through sintering so greatly that an undesired reaction upon the specific magnetic values is produced, which can be explained, according to present-day knowledge of the connections between the grain size of such powders and their permanent-magnetic properties, by

this increase in the grain size. In experiments regarding the possibilities of working-up such oxide powders while avoiding these reactions, it has now surprisingly been found that where the oxide powder, being given a high magnetic value in a suitable manner, is bound by synthetic resin or similar binding agents, in contrast to the binding of permanent magnets of other materials with synthetic resin, practically the same magnetic values as in the case of sintered pulverulent bodies are obtained. This effect is clearly discernible with these materials even on the use of very small orienting fields, and in some circumstances even where these fields are completely dispensed with.

I claim:

1. A method of producing a permanent magnet, com prising the steps of sprinkling a mixture of pulverulent particles of anisotropic permanent magnet material and a binding agent into a mold so that said mixture falls freely for a predetermined distance into said mold; sub jecting said mixture while the same is falling freely into said mold to the action of a magnetic field of predetermined constant direction so that said particles of permanent magnet material are oriented while falling freely before settling in said mold; thereby forming in said mold' a mass of said mixture the particles of permanent magnet materi-al of which are substantially all magnetically oriented; and pressing said mass into a coherent magnetic body.

2. A method of producing a permanent magnet, comprising the steps of sprinkling a mixture of pulverulent particles of anisotropic permanent magnet material and a binding agent into a mold so that said mixture falls freely for a predetermined distance into said mold; subjecting said mixture while the same is falling freely into said mold to the action of a magnetic field of predetermined constant direction so that said particles of permanent magnet material are oriented while falling freely before settling in said mold; thereby forming in said mold a mass of said mixture the particles of permanent magnet material of which are substantially all magnetically oriented; pre-tableting said mass in said mold under the action of said magnetic field; and pressing the thus pre tableted mass into a coherent magnetic body.

3. A method of producing a permanent magnet, comprising the steps of sprinkling a mixture of pulverulent particles of anisotropic permanent magnet material and a binding agent into a mold so that said mixture falls freely for a predetermined distance into said mold; sub jecting said mixture while the same is falling freely into said mold to the action of a magnetic field of predetermined constant direction so that said particles of permanent magnet material are oriented while falling freely before settling in said mold; thereby forming in said mold a mass of said mixture the particles of permanent magnet material of which are substantially all magnetically oriented; pre-tableting said mass in said mold into a predetermined magnet shape under the action of said magnetic field, the direction of pressing for the pre-tableting being in a direction perpendicular to the plane of said magnetic field; and pressing the thus pre-tableted mass into a final coherent magnetic body.

4. A method of producing a permanent magnet, comprising the steps of sprinkling a mixture of pulverulent particles of anisotropic permanent magnet material and a binding agent into a mold so that said mixture falls freely for a predetermined distance into said mold; subjecting said mixture while the same is falling freely into said mold to the action of a magnetic field of predetermined constant direction so that said particles of permanent magnet material are oriented while falling freely before settling in said mold; thereby forming in said mold a mass of said mixture the particles of permanent magnet material of which are substantially all magnetically oriented; pre-tableting said mass in said mold into a predetermined magnet shape under the action of said magnetic field, the direction of pressing for the pre-tableting being in a direction perpendicular to the plane of said magnetic field; consolidating a plurality of thus pretableted masses; and pressing said plurality of pre-tableted masses into a single coherent magnetic body.

5. A method of producing a permanent magnet, comprising the steps of sprinkling a mixture of pulverulent particles of anisotropic permanent magnet material and a binding agent into a mold so that said mixture falls freely for a predetermined distance into said mold; subjecting said mixture while the same is falling freely into said mold to the action of a magnetic field of predetermined constant direction so that said particles of permanent magnet material are oriented while falling freely before settling in said mold; thereby forming in said mold a first layer of said mixture the particles of permanent magnet material of which are substantially all magnetically oriented; pressing said first layer into a first coherent layer; sprinkling additional mixture of pulverulent particles of anisotropic permanent magnet material and binding agent into said mold on said first coherent layer so that said mixture falls freely for a predetermined distance into said mold; subjecting the thus falling mixture to the action of said magnetic field so that said particles of permanent magnet material are oriented While falling freely before settling in said mold; thereby forming in said mold on said first coherent layer an additional layer of said mixture the particles of permanent magnet material of which are substantially all magnetically oriented; pressing said additional layer into a coherent magnetic layer coherent with said first coherent magnetic layer; and repeating said sprinkling of said mixture, subjecting the mixture to said magnetic field and said pressing until a coherent magnetic body of predetermined dimensions is formed.

6. A method of producing a permanent magnet, comprising the steps of sprinkling a mixture of pulverulent particles of anisotropic permanent magnet material and a binding agent into a mold so that said mixture falls freely for a predetermined distance into said mold; subjecting said mixture While the same is falling freely into said mold to the action of a magnetic field of predetermined constant direction so that said particles of permanent magnet material are oriented while falling freely before settling in said mold; thereby forming in said mold a first layer of said mixture the partices of permanent magnet material of which are substantially all magnetically oriented; compressing said layer; sprinkling additional mixture of pulverulent particles of anisotropic permanent magnet material and binding agent into said mold on the thus compressed layer so that said mixture falls freely for a predetermined distance into said mold; subjecting the thus falling mixture to the action of said magnetic field so that said particles of permanent magnet material are oriented while falling freely before settling in said mold; thereby forming in said mold on said compressed first layer an additional layer of said mixture the particles of permanent magnet material of which are substantially all magnetically oriented; compressing said additional layer on said first compressed layer; repeating said sprinkling of said mixture, subjecting said mixture to said magnetic field and compressing of the formed layer until a body of predetermined height is formed; and pressing the thus formed body into a coherent magnetic body.

7'. A method of producing a permanent magnet, comprising the steps of sprinkling a mixture of pulverulent particles of anisotropic permanent magnet material and a binding agent into a mold so that said mixture falls freely for a predetermined distance into said mold; subjecting said mixture while the same is falling freely into said mold to the action of a magnetic field of predetermined constant direction so that said particles of permanent magnet material are oriented while falling freely before settling in said mold; thereby forming in said mold a mass of said mixture the particles of permanent magnet material of which are substantially all magnetically oriented; and pressing said mass into a coherent magnetic body, the direction of pressing of said mass being substantially transverse to the direction of said magnetic field.

8. A method of producing a permanent magnet, comprising the steps of sprinkling a mixture of pulverulent particles of anisotropic permanent magnet material consisting of an alloy selected from the group consisting of Al-Ni and Al-Ni-Co alloys and a binding agent into a mold so that said mixture falls freely for a predetermined distance into said mold; subjecting said mixture while the same is falling freely into said mold to the action of a magnetic field of predetermined constant direction so that said particles of permanent magnet material are oriented 'while falling freely before settling in said mold; thereby forming in said mold a mass of said mixture the particles of permanent magnet material of which are substantially all magnetically oriented, and pressing said mass into a coherent magnetic body.

9. A method of producing a permanent magnet, comprising the steps of sprinkling a mixture of pulverulent particles of anisotropic permanent ferromagnetic material having a particle size of less than 0.1,u. and a binding agent into a mold so that said mixture falls freely for a predetermined distance into said mold; subjecting said mixture while the same is falling freely into said mold to the action of a magnetic field of predetermined constant direction so that said particles of permanent magnet material are oriented while falling freely before settling in "said mold; thereby forming in said mold a mass of said mixture the particles of permanent magnet material of which are substantially all magnetically oriented; and pressing said mass into a coherent magnetic body.

10. A method of producing a permanent magnet, comprising the steps of sprinkling a mixture of pulverulent particles of anisotropic permanent magnet material consisting of a metallic oxide and a binding agent into a mold so that said mixture falls freely for a predetermined distance into said mold; subjecting said mixture while the same is falling freely into said mold to the action of a magnetic field of predetermined constant direction so that said particles of permanent magnet material are oriented while falling freely before settling in said mold; thereby forming in said mold a mass of said mixture the particles of permanent magnet material of which are substantially all magnetically oriented; and pressing said mass into a coherent magnetic body.

11. A method of producing a permanent magnet, comprising the steps of sprinkling a mixture of pulverulent particles of anisotropic permanent magnet material consisting of a mixture of Al-Ni alloy, Al-Ni-Co alloy, ferromagnetic material and metallic oxides and a binding agent into a mold so that said mixture falls freely for -a predetermined distance into said mold; subjecting said mixture while the same is falling freely into said mold to the action of a magnetic field of predetermined constant direction so that said particles of permanent magnet material are oriented while falling freely before settling in said mold; thereby forming in said mold a mass of said mixture the particles of permanent magnet material of which are substantially all magnetically oriented; and pressing said mass into a coherent magnetic body.

12. A method of producing a permanent magnet, comprising the steps of sprinkling a mixture of pulverulent particles of anisotropic permanent magnet material consisting of a metallic oxide and a binding agent into a moldso that said mixture falls freely for a predetermined distance into said mold; subjecting said mixture while the same is falling freely into said mold to the action of a magnetic field of predetermined constant direction so that said particles of permanent magnet material are oriented while falling freely before settling in said mold; thereby forming in said mold a mass of said mixture the particles of permanent magnet material of which are substantially all magnetically oriented; pressing said mass into a coherent magnetic body; subjecting said mass under the action of said magnetic field to a heat treatment; and pressing the thus treated mass into a coherent magnetic body.

13. A method according to claim 10 in which said magnetic material is pressed into a body in said mold at below the sintering temperature of said metallic oxide while the intensity of said magnetic field is substantially zero.

References Cited in the file of this patent UNITED STATES PATENTS Re. 20,507 Andrews et al. Sept. 14, 1937 1,974,079 Maier Sept. 18, 1934 1,976,230 Kato et a1. Oct. 9, 1934 1,981,468 Roseby Nov. 20, 1934 1,994,534 Robinson Mar. 19, 1935 2,064,773 Vogt Dec. 15, 1936 2,185,138 Wolif Dec. 26, 1939 2,188,091 Baermann Jan. 23, 1940 2,221,983 Mayer et a1. Nov. 19, 1940 2,576,679 Guillaud Nov. 27, 1951 FOREIGN PATENTS 146,344 Australia May 6, 1952 

